A capacitive MEMS pressure sensor requires two electrodes that move relative to each other under an applied pressure. This configuration is most often accomplished by having a fixed electrode (hereafter called the lower electrode) formed in a substrate while a moveable electrode (hereafter called the upper electrode) is provided in a deformable membrane which is exposed to the pressure that is to be sensed. One or more of the electrodes are typically formed by deposition of a conductive film, electrical isolation of a conductive layer, or by simply adding a spacer layer between two conductive materials.
In capacitive MEMS pressure sensors that incorporate a deposited epi-polysilicon layer to form the deformable membrane, dielectric spacers are typically used to isolate the upper electrode within the membrane. A pressure sensor with this electrode configuration can then be stacked on top of pre-existing structures to create wafer-scale encapsulation processes that are capable of producing a wide range of devices. In these fabrication iterations, however, silicon nitride dielectric spacers are typically used to provide the electrode isolation.
What is needed, therefore, is a capacitive pressure that does not require additional materials to provide the electrical isolation between the electrodes. In addition, a method of producing such a capacitive pressure sensor that incorporates existing epitaxial silicon wafer-scale encapsulation techniques would be beneficial.